Hybrid spread spectrum radio system

ABSTRACT

Systems and methods are described for hybrid spread spectrum radio systems. A method includes modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control an amplification circuit that provides a gain to the signal. Another method includes: modulating a signal by utilizing a subset of bits from a pseudo-random code generator to control a fast hopping frequency synthesizer; and fast frequency hopping the signal with the fast hopping frequency synthesizer, wherein multiple frequency hops occur within a single data-bit time.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY-SPONSOREDRESEARCH AND DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC05-00OR22725 between the United States Department ofEnergy and UT-Battelle, LLC.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of communications. Moreparticularly, the invention relates to spread-spectrum communications.

2. Discussion of the Related Art

Conventional radio-frequency (RF) digital-data transmission schemes arein general highly susceptible to errors caused by multipath propagationand other interference conditions. Historically, direct-sequencespread-spectrum techniques have offered reasonably good immunity againstlong-path (e.g. outdoor) types of reflections, where the timedistribution (dispersion) of the arrival of the individual successivesignal reflections is generally greater than the effective chippingperiod (inverse of the spread-spectrum chipping rate) of the transmittedsignal.

Outdoor environments often exhibit delay-dispersion profiles in therange of 3-100 μs (typically ˜25 μs RMS maximum [for hilly terrain]) andthus are generally addressed with signal spreading rates of ˜1Mchips/sec (especially when used with time-offset quadrature modulationschemes such as OQPSK); these are in fact very close to the existingparameters of the IS-95 CDMA cellular-telephone system in wide usethroughout the U.S. and in many other countries.

For the indoor propagation case, however, the dispersion times are muchshorter—typical figures range from 10 to 250 ns, with a median RMSdispersion value of 50 ns. The longer values would imply a minimumspreading rate of ˜4 Mchips/sec, while the shorter (worst-case) valuescall for spreading rates of about 100 Mchips/sec (and, thus, at least100 MHz of signal bandwidth for standard direct-sequence (DS) signalsusing conventional binary phase-shift keying (BPSK) or frequency-shiftkeying (FSK) modulation. For OQPSK schemes as mentioned above, theminimum required bandwidth is halved but is still nevertheless veryunwieldy in crowded RF bands.

Obviously, this bandwidth is not reasonably obtainable in any of theavailable Industrial, Scientific, and Medical (ISM) bands currentlyallocated for spread-spectrum transmission in the U.S. below 5 GHz (andwould require the whole available 100-MHz band for ISM and UnlicensedNational Information Infrastructure [U-NII] applications above 5 GHz),so other techniques must be applied to overcome the multipath problemfor indoor wireless links. One prevalent option is to employ frequencyhopping, so that via the periodic carrier-frequency changes, the signalwill hop to frequencies which do not exhibit multipath nulls(destructive interferences) from the transmitter at the desiredreceiving points. In general, the total received RF energy of many ofthese data bursts (hops) will be cancelled by the nulls (and thusproduce, bad data packets), but generally a majority will be ofsatisfactory quality to provide reasonably effective link operation.

However, either complex (and delay-inducing) interleaving and/orerror-correction coding algorithms (e.g., Reed-Solomon) must beintroduced into the link, or numerous packet retransmissions will berequired to successfully transport the data payload. In either case,significant levels of latency and concurrent link-rate limitations willinevitably result.

Some methodologies have even been developed to build “hopping tables” ofuseable (low-error) frequencies in the system-control software, andthereby avoid the frequencies with propagation nulls, but in general asthe signal-transmission environment changes with movements of equipment,personnel, and RF interference sources, the set of “bad” frequencieswill need to be constantly updated; even so; statistically andpractically, some bad packets will nevertheless always be received.Furthermore, the use of “intelligent” hopping schemes which on averageavoid certain hopping channels in a coordinated fashion have beenhistorically disallowed by the Federal Communications Commission (FCC)on the ISM bands, since the average channel occupancy would benonuniform and thereby skew the normal long-term random signal-frequencystatistics intended for ISM-band frequency-hopping system operation,resulting in a statistical increase in interference to other users(although via rules changes by the FCC in the last few months, thisprohibition has been somewhat relaxed). Overall, however, this scheme,although usually workable for fixed devices, generally fails in mobileapplications or when the RF environment is dynamic, since the positionsof the multipath nulls (and thus the sets of “bad” channels) areconstantly changing.

Heretofore, the requirements of a more robust scheme (fewer data errors)which will function effectively even in severe multipath environments(e.g., highly RF-reflective areas) and yet avoid the introduction ofeither extremely complex error-correction hardware with substantiallatency (delay) into the transmission process and/or the-requirement forfrequent retransmissions, plus offering a solution to the issue of linklatencies (which can be particularly significant in high-speed controlapplications where the delays can cause loop-stability problems for theRF-in-the-loop systems referred to above) have not been fully met. Foroperation in the United States, the scheme must additionally comply withFCC Part 15 regulations for the ISM and U-NII bands by guaranteeingadequately random spectral characteristics of its transmissions at alltimes.

Still another essential aspect of modem RF telemetry systems is that ofefficient power utilization. It is desirable to operate many distributeddevices, including sensors, alarm systems, RFID tags, and the like fromlow-cost, compact battery sources for maintenance-free intervals of 1 toabout 5 years (or even longer). It is therefore highly desirable toprovide a system RF telemetry-protocol which achieves reliable datatransmission with an absolute minimum of remote-device powerconsumption.

Yet another critical need in many systems is to simultaneously operate alarge number of RF devices (such as tags, sensors, and the like) in aproximal area without significant-statistical levels of mutualinterference; in common parlance, this is the familiar multiple-accessproblem which is handled by well known frequency-, time-, orcode-division multiplexing or multiple-access techniques (typicallyreferred to as FDMA, TDMA, and CDMA, respectively). However, thesemethods have not hitherto been simultaneously employed in a programmablyor adaptively coupled or coordinated fashion to provide a usefulincrease in the permissible number of devices operable in a given areafor a specific amount of mutual interference.

Still another need is for an RF signal-transmission technique which evenin the presence of multipath and multi-user interference can support anaccurate radiolocation function where the respective locations of the RFdevices can be readily detected, such as for equipment, container, andpersonnel tracking.

Another key need is for an RF signaling protocol which offers improvedtransmission security against reception, decoding, or even detection byunauthorized parties.

Finally, a need exists for an RF signaling technique which also providesa high degree of signal programmability and adaptability to rapidlyaccomplish tradeoffs in the DS code lengths, frequency- and time-hoppingpatterns, and the interrelationships thereof to effectively addressdynamic signal and device-use conditions (e.g., changing multipath andRFI conditions and system functional requirements).

What is needed, then, is a solution that addresses all of theserequirements.

SUMMARY OF THE INVENTION

There is a need for the following embodiments. Of course, the inventionis not limited to these embodiments.

According to a first aspect of the invention, a method comprises:modulating a signal by utilizing a subset of bits from a pseudorandomcode generator to control an amplification circuit that provides a gainto the signal. According to a second aspect of the invention, anapparatus comprises: a pseudorandom code generator; and an amplitudecontroller coupled to the pseudorandom code generator. According to athird aspect of the invention, a method comprises: directly synthesizinga digital signal including: amplitude modulating an output channel witha four-quadrant amplitude multiplier to provide an amplitude ditheredsignal. According to a fourth aspect of the invention, an apparatuscomprises a direct digital synthesizer including a four-quadrantamplitude multiplier, wherein the direct digital synthesizer provides anamplitude dithered signal. According to a fifth aspect of the invention,a method comprises: directly synthesizing a digital signal including:amplitude modulating an “in-phase” (I) channel with a firstfour-quadrant amplitude multiplier; and amplitude modulating a“quadrature-phase” (Q) channel with a second four-quadrant amplitudemultiplier. According to a sixth aspect of the invention, an apparatuscomprises: a direct digital synthesizer including a first four-quadrantamplitude multiplier and a second four-quadrant amplitude multiplier,wherein the first four-quadrant amplitude multiplier and the secondfour-quadrant amplitude multiplier are coupled together in parallel.According to a seventh aspect of the invention, a method comprises:modulating a signal by utilizing a subset of bits from a pseudo-randomcode generator to control a fast hopping frequency synthesizer; and fastfrequency hopping the signal with the fast hopping frequencysynthesizer, wherein multiple frequency hops occur within a singledata-bit time. According to an eight aspect of the invention, anapparatus comprises: a pseudo-random code generator; and a fast hoppingfrequency synthesizer coupled to the pseudo-random code generator,wherein multiple frequency hops occur within a single data-bit time.

These, and other, embodiments of the invention will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingvarious embodiments of the invention and numerous specific detailsthereof, is given by way of illustration and not of limitation. Manysubstitutions, modifications, additions and/or rearrangements may bemade within the scope of the invention without departing from the spiritthereof, and the invention includes all such substitutions,modifications, additions and/or rearrangements.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings accompanying and forming part of this specification areincluded to depict certain aspects of the invention. A clearerconception of the invention, and of the components and operation ofsystems provided with the invention, will become more readily apparentby referring to the exemplary, and therefore nonlimiting, embodimentsillustrated in the drawings, wherein like reference numerals (if theyoccur in more than one view) designate the same elements. The inventionmay be better understood by reference to one or more of these drawingsin combination with the description presented herein. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale.

FIG. 1 illustrates a block schematic view of a hybridfrequency-hopping/direct-sequence spread-spectrum transmitter(BPSK-modulated), representing an embodiment of the invention.

FIG. 2 illustrates a block schematic view of a hybridfrequency-hopping/direct-sequence spread-spectrum receiver(BPSK-modulated), representing an embodiment of the invention.

FIG. 3 illustrates a block schematic view of a hybridtime-hopping/direct-sequence spread-spectrum transmitter, representingan embodiment of the invention.

FIG. 4 illustrates a block schematic view of a hybridtime-hopping/direct-sequence spread-spectrum receiver, representing anembodiment of the invention.

FIG. 5 illustrates a block schematic view of a hybridfrequency-hopping/time-hopping/direct-sequence spread-spectrumtransmitter, representing an embodiment of the invention.

FIG. 6 illustrates a block schematic view of a hybridfrequency-hopping/time-hopping/direct-sequence spread-spectrum receiver,representing an embodiment of the invention.

FIG. 7 illustrates a block schematic view of a hybrid programmabledirect-digital synthesizer (DDS) transmitter, representing an embodimentof the invention.

FIG. 8 illustrates a block schematic view of a hybrid programmabledirect-digital synthesizer (DDS) transmitter with external interface,representing an embodiment of the invention.

FIG. 9 illustrates a block schematic view of an RF upconverter circuit,representing an embodiment of the invention.

FIG. 10 illustrates a block schematic view of an alternate RFupconverter circuit, representing an embodiment of the invention.

FIG. 11 provides a block diagram of an RF transmitter systemincorporating an RF signal polarization-control circuit, representing anembodiment of the invention.

FIG. 12 provides a block diagram of an RF receiver system correspondingto the transmitter of FIG. 11, which incorporates polarization-diversityreception capability, representing an embodiment of the invention.

FIG. 13 illustrates a typical indoor RF propagation environment via itscharacteristic signal-delay profile.

FIG. 14 depicts a representative moderately sharp multipath cancellationnull typical of indoor RF environments, with a superimposed set of fivehybrid spread-spectrum signals of medium bandwidth, representing anembodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention and the various features and advantageous details thereofare explained more fully with reference to the nonlimiting embodimentsthat are illustrated in the accompanying drawings and detailed in thefollowing description. Descriptions of well known components andprocessing techniques are omitted so as not to unnecessarily obscure theinvention in detail. It should be understood, however, that the detaileddescription and the specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only andnot by way of limitation. Various substitutions, modifications,additions and/or rearrangements within the spirit and/or scope of theunderlying inventive concept will become apparent to those skilled inthe art from this detailed description.

The below-referenced U.S. Patents disclose embodiments that weresatisfactory for the purposes for which they are intended. The entirecontents of U.S. Pat. Nos. 6,556,942; 5,623,487; 5,521,937; 5,274,665;and 4,550,292 are hereby expressly incorporated by reference herein forall purposes. The entire contents of allowed U.S. patent applicationSer. No. 09/671,636, filed Sep. 27, 2000, in which the issue fees havebeen paid, are hereby expressly incorporated by reference herein for allpurposes.

The invention can include the specific code-related combination ofstandard direct-sequence (DS) spread-spectrum (SS) modulation with“fast” frequency hopping (FFH), wherein multiple frequency hops occurwithin a single data-bit time. Specifically, the most significantbenefit to fast frequency hopping is that each bit is represented bychip transmissions at multiple frequencies. If one or more chips arecorrupted by multipath or interference in the RF link, statistically amajority should still be correct. Indeed, with suitable error detection,if even one chip is correct, the original data bit can still berecovered correctly. [Standard or “slow” frequency hopping (SFH orsimply FH), in contrast, transmits at least one and usually several databits in each hopping interval.] In the invention, alternatively, forexample, the hopping can be augmented or replaced by frequency sweeps or“chirps” of an unconstrained or constrained (i.e., continuous-frequencyand/or continuous-phase) nature. The difficult indoor RF propagationenvironments typical of offices and large industrial spaces dictate thathighly robust techniques are necessary for good link performance. Themultiple signal reflections cause significant deterioration ofconventional signals and attendant high data-error rates. The temporalplot of FIG. 13 illustrates a typical indoor RF propagation environmentvia its characteristic signal-delay profile. Note that the RMS delayspread (the time signal reflections from the walls, ceiling, and floorare still arriving at the antenna) is nearly 50 ns; without special RFsignaling techniques, this will cause major data errors unless theinformation rate is very low. Even conventional spread-spectrum linkswill need greater than 20 MHz of bandwidth for successful operation inthis venue. The effect of multipath can also be clearly seen in thefrequency-domain plot of FIG. 14, which depicts a representativemoderately sharp multipath cancellation null (typical of indoor RFenvironments) near the center of signal band {circle around (3)}, with asuperimposed set of five hybrid spread-spectrum signals of mediumbandwidth ({circle around (1)} through {circle around (5)}). Due to thepropagation null, signal band {circle around (3)} is essentiallyblocked, bands {circle around (2)} and {circle around (4)} are somewhatattenuated (and distorted due to the spectral tilting), while bands{circle around (1)} and {circle around (5)} largely unaffected. Clearly,by using multiple frequencies, the probability of getting the datathrough correctly is much greater than in conventional systems.

A significant further advantage of the fast-hopping aspect of theinvention is that of multipath “avoidance”: this can be appreciated byobserving that in a multiple-reflection environment as depicted in FIG.13, if the time between successive signal hops is less than that betweenthe successively received reflections, then there will be very littleopportunity for the later signal arrivals to cause destructiveinterference when combined with the earlier paths; this, of course can(depending on the particular delay profile of the area) require fairlyhigh hopping rates, though this requirement can also be somewhatameliorated by the presence of the DS component in the composite HSSsignal.

Still another aspect of the invention is in the high degree ofprogrammability of the different facets of the HSS signal in thepreferred implementations; here, the complete software/firmwaredirection of the DS spreading (chipping) rate, the FH hopping rate,carrier frequencies, and time/frequency profiles, plus the interrelatedor independent time-hopping (TH) and/or polarization control, providesan hitherto unattainable degree of signal programmability andadaptability to rapidly and efficiently accomplish tradeoffs in the DScode lengths, frequency- and time-hopping patterns, signal polarization,and the interrelationships thereof to effectively address dynamic signaland device-use conditions (e.g., changing multipath and RFI conditionsand system functional requirements).

Excellent signal security is another advantage of the invention: sinceso many signal parameters can change in a rapid fashion, and sincesuccessful synchronization requires substantial a priori knowledge ofthe code relationships between the DS, FH, TH, and polarizationcomponents of the HSS signal, the unintended listener will experiencegreat difficulty in fully synchronizing with the HSS transmission anddecoding the embedded data. An even higher level of HSS signal securitycan be achieved by dynamically altering the PN code relationships withinthe HSS transmitter; this can take the form of rolling code segments,scrambling of the code vectors, or table-based reassignments of thebit-pattern relationships. Obviously, the degree of difficulty inintercepting such a complex transmission without the required code“keys” or indices is extreme; of course, standard data-encryptiontechniques may also be added in addition to the above to provide evengreater security of the transmitted data.

Still another major issue solved by the invention is that of efficientmultiple access: in a proximal area, often dozens to hundreds or eventhousands of devices (e.g., wireless sensor nodes, RFID tags, alarmunits, and the like) are required to interoperate without significantdata loss due to RF interference, multipath, or collisions from-otherdevices in the group. Appropriately programmed HSS can-exhibit superiormultiple-access performance to even full power-controlled CDMA systems(e.g., cell phones) due to the concatenation of DS-CDMA techniques withthe additional dimensions of the FH and TH modulations. These addedsignal dimensions permit greater diversity, access for more users,and/or can substantially ease the need for high accuracy in the CDMApower-control function. Moreover, the improved flexibility of theinvention can support transmit-only devices which cannot bepower-controlled and thus are not amenable to operating in a trueCDMA-only environment. Since the multiple-access interference caused bythe uncontrolled power levels of these units quickly exceeds tolerablelimits for CDMA operation, especially with varying device locations(and, thus, the classic near-far problem for DS systems), the HSSprotocol of the invention offers an effective means of accommodatingsuch uncontrolled, randomly transmitting one-way units without adverselyaffecting the overall system multiple-access operations. This isprincipally accomplished by assigning specific CDMA codes to suchdevices and constraining their hopping frequency and time sequences tostatistically avoid the more conventional (power-controlled) units'transmission slots.

In addition, to provide higher performance in typical multipath-proneindustrial, military, and commercial wireless signal propagationenvironments, the capability to perform a continuous-phase (CP)synthesis of the combined DS/FFH signal waveform permits more effectiveutilization of RF spectrum (narrower bandwidth control and avoidance oftransient spectral “splatter”) and simultaneously the potential forfaster, more stable receiver synchronization in adverse transmissionenvironments.

A further aspect of the invention is the application of statisticallyamplitude-dithered modulation and/or statistical polarization control ofthe combined CP-DS/FFH signal via pseudorandom-polynomial techniques toprovide even more immunity to multipath-induced signal cancellations,which typically cause dropouts and accompanying high rates of dataerrors. The use of amplitude dithering minimizes the effect ofsuccessive chip cancellations due to closely spaced destructive signalreflections in low-loss (e.g., metal-walled) RF environments. It can beused to perturb or “break up” multipath-induced signal nulls where thesignal is effectively cancelled by the destructive interferences due tounfortunate combinations of multiple reflected signals from diversepaths. When the vector sum of the multiple components approaches zero,by rapidly changing the amplitude of the transmitted signal (within thetime-frame of the successively received reflection signals), thecancellation of the multiple-path signals can at least partially be“undone”, leaving a reasonable amount of instantaneous signal amplitudeat the receiver to decode. To achieve maximum error-reduction benefitindependently from this amplitude-dithering technique, the time rate ofdithering (amplitude changing) should be at least comparable to the rateof arrival of successive reflected signals at the designated receiver(and ideally somewhat greater); this, in turn, still requires a fairlyhigh dither rate unless combined with other aspects of the invention.

The application of PN-code controlled polarization control, whenproperly synchronized between transmitter and receiver(s), provides evengreater signal diversity and, thus, immunity against multipath-inducedsignal nulls and dropouts (as well as unauthorized signal reception).This is accomplished by altering the transmitted signal wavepolarization as a function of a specified PN code; with differentorientations of the signal electric (E) and magnetic (H) fields, therespective reflection coefficients at room boundaries and otherinterfaces will also change, thus shifting (or “dithering”) themultipath null depths, frequencies, and locations. As will be describedin later examples, the programming of the effective transmitted signalpolarization can be accomplished by the concurrent control of therelative ratio of the power sent to two orthogonally polarized antennas,typically one vertical and the other horizontal.

Often the concatenation of some, most or all of the aforementionedmethodologies will be required to provide a highly reliable linksuitable for critical commercial, industrial and/or militaryapplications in adverse (i.e., multipath- and interference-prone) RFenvironments. Although there are a multitude of possible specificboard-level implementations of the hybrid spread-spectrum (HSS)modulator and/or demodulator, the most practical, compact, andcost-effective form is certainly that involving highly integrated customintegrated-circuit (IC) chip(s) to achieve the desired systemfunctionality, programmability, size and reasonable power consumptioncharacteristics at a usefully low cost.

All the aforementioned features (with the possible exception-of theantenna polarization control at higher power levels) can be readilyimplemented in monolithic integrated-circuit form to provide a highlyrobust, low-cost digital transmission device for a multitude ofindustrial, commercial and military wireless applications.

Numerous direct-digital synthesizers (DDS) devices have appeared on themarket which are generally suitable to form the core of a practicalhybrid spread-spectrum transmission system according to the presentinvention, although obviously none can simultaneously achieve all of therequired functions. Perhaps the closest commercially available device sofar is the Analog Devices AD9854, which includes a continuous-phase RFfrequency synthesizer which can be frequency-ramped or swept and/ordownstream phase-modulated as desired. The digitally modulated carrierphase data is internally converted to parallel in-phase (“I”) andquadrature-phase (“Q”) digitized waves. Each is optionally passedthrough an inverse-sinc response FIR filter (to compensate for thefrequency-response deviations caused by the signal sampling/digitizationprocess) and a downstream amplitude-control multiplier and finallyconverted to analog voltages by a pair of high-speed digital-to-analogconverters (DACs).

Unfortunately, several features needed to fully synthesize the HSSformat are not included in the AD9854 (or any other currently availablecommercial device, either); these include separate phase-modulatorblocks upstream from the I and Q phase-to-amplitude converters [sine-and cosine-formatted read-only memory (ROM) blocks]; full four-quadranthigh resolution (e.g., 14-bit or better) amplitude modulators(multipliers) ahead of the DACs, or alternatively, high-accuracytwo-quadrant multiplying DAC structures; a fast, wide (i.e., 32-bit orgreater) parallel programming and data interface to support highchipping rates and/or hopping/chirping rates; and sufficient faston-chip parameter caching to complement the parallel interface speed andthereby achieve the desired rapid (i.e., ≧10-MHz) internal synthesizerparameter reprogramming rates.

A practical, moderately fast HSS system implementation achievable withcurrently available devices includes: an AD9854; standard clockcircuitry; an external DSP control device, high-speed field-programmablegate arrays (FPGAs) for parallel data interfacing; two fast externaldownstream analog multipliers (e.g., Analog Devices AD834s); and a finalRF output signal combiner to sum the I- and Q-channel modulated signalsfrom the multipliers. With a 300-MHz version of the AD9854 chip, RFoutput bandwidths of up to 120 MHz are achievable for wideband I/Qupconversion to a convenient RF transmission band; alternatively, astandard but wide-bandwidth surface acoustic wave (SAW) IF bandpassfilter (e.g. 36-MHz width at a 70-MHz center frequency) can be employedwith a separate frequency-synthesized upconverter to produce thegenerally higher spans required to cover the standard 2.45- and 5.7-GHzISM and the 5.1- and 5.3-GHz U-NII unlicensed RF transmission bands.(For the narrower 902-928 MHz ISM band, a simple fixed upconverter couldbe substituted for the separate synthesizer stage.)

EXAMPLES

Specific embodiments of the invention will now be further described bythe following, nonlimiting examples which will serve to illustrate insome detail various features. The following examples are included tofacilitate an understanding of ways in which the invention may bepracticed. It should be appreciated that the examples which followrepresent embodiments discovered to function well in the practice of theinvention, and thus can be considered to constitute preferred modes forthe practice of the invention. However, it should be appreciated thatmany changes can be made in the exemplary embodiments which aredisclosed while still obtaining like or similar result without departingfrom the spirit and scope of the invention. Accordingly, the examplesshould not be construed as limiting the scope of the invention.

Example 1

Referring to FIGS. 1-2, a hybrid frequency-hopping/direct-sequence(FH/DS) spread-spectrum scheme is depicted.

A hybrid frequency-hopping/direct-sequence (FH/DS) spread-spectrumtransmitter depicted in FIG. 1 is configured for standard BPSK datamodulation. A subset of m bits from the full n-bit (n>m) PN code is usedin synchronization with the chipping sequence to drive an RF synthesizer100 to generate the exact RF carrier frequency desired for the hybrid SStransmission. Note that an additional p higher-order bits in the RFsynthesizer (DDS) frequency-control word are used to specify the RFoperating band; the lower-order m bits from the PN register select theindividual hopping channels. The precise mapping of hopping frequenciesin the RF synthesizer 100 can be handled straightforwardly via a ROM mapor within an FPGA or equivalent device. The latter-implementations areparticularly useful when implementing fast frequency hopping or for veryhigh data throughput and/or chipping rates.

An amplitude control 110 depicted can be directly applied (as shown) tomodulate or control the transmitter final RF output power; additionallyor alternatively, the dithered amplitude data, generally obtained as klines (parallel bits) from the PN generator, can be used to control feedpower levels to antennas of orthogonal polarizations (i.e., horizontaland vertical) to provide improved signal diversity in the RFenvironment, as also depicted in FIG. 11. There are numerous possibleimplementations of this amplitude control, including (but not limitedto) classical high- and low-level AM modulators, pulse-width modulation(PWM) control of the supply voltage feeding the final RF amplifier(s),transformer-summed Class-C or -E amplifier stages, and so forth.Alternatively, any incidental amplitude variations in the output signalare often undesirable for many environments, and constant-envelopemodulation techniques are to be preferred where higher RFpower-amplifier efficiency (e.g., Classes C, D, E, F, or S) is desired.Further, in high-multipath scenarios, a constant-envelope transmittedHSS signal will permit improved signal processing by the receiver, asexplained later in the text describing FIG. 12.

The corresponding hybrid FH/DS spread-spectrum receiver architecture isshown in FIG. 2. Here, the incoming hybrid signal is amplified in afront-end low-noise amplifier (LNA) 200, down-converted to the desiredintermediate frequency (F) via a balanced mixer 210, amplified andbandpass filtered in a bandpass amplifier (BPA) block 220, and finallydemodulated in a conventional manner via a typical bit-wisematched-filter or correlator structure 230. As in the transmitter above,m bits from the n-bit PN code generator (though typically offset by afixed amount from those in the transmitter to provide the desired IFdifference frequency) are used to select the desired hopping channelswithin the selected RF receiving band.

A fixed local-oscillator signal is used to up-convert (preferably in animage-cancelling, single-sided [“SSB”] mode) the synthesizer outputfrequency to the appropriate value to produce the target IF; this finalprogrammable FH/DS local oscillator signal is modulated by the PNpolynomial code sequence and applied to the balanced mixer 210. Thisspread signal is then (when properly synchronized) automaticallydespreads the DS portion of the incoming hybrid signal; the hopping ofthe local signal also removes the FH component, leaving a simpledata-modulated single-frequency signal at the input to the bandpass IFamplifier chain 220. Synchronization for the system is derived from thedata stream, the RF carrier frequency, or a combination thereof. Anoptional multipath-amplitude detector block 240 can provide a relativemeasurement of the amount of multipath-caused disturbances in thereceived signal. This is typically implemented via detection ofvariations in the received-signal's envelope (amplitude), which areutilized by separate signal-processing circuitry to estimate themultipath-induced degradations in the incoming signal and perform atleast a first-order cancellation thereof to improve final data qualityat the receiver's output.

Example 2

Referring to FIGS. 3-4, a hybrid time-hopping/direct-sequence (TH/DS)spread-spectrum scheme is depicted.

A hybrid time-hopping/direct-sequence (TH/DS) spread-spectrumtransmitter is represented by FIG. 3. Here, as in the previous TH/DStransmitting scheme, the main PN code generator 300 of n bits alsoprovides a subset of m bits to a pattern-detecting coincidence gate 310.When the selected m-bit pattern is recognized, a data-gate control unit330 gates a burst of data bits into the DS spreader (via an exclusive-ORgate 340 feeding a balanced modulator 350). Simultaneously, a trigger(“T”) flip-flop 360, in essence driven by the coincidence output line,gates on a final RF power amplifier 370 for the prescribed interval(plus small power-up and power-down times) to complete the time-hoppedburst transmission.

The corresponding hybrid TH/DS spread-spectrum receiver architecture isshown in FIG. 4. Here, the TH/DS receiver is similar to the FH/DSreceiver unit described earlier, except that the m bits extracted from amaster PN generator 400 drive a coincidence detector 410 like the one inthe transmitter above rather than a frequency synthesizer. A “T”flip-flop 420 in this case, once the system is synchronized, simplygates off the RF input until the desired time slot occurs, whichminimizes receiver operating power requirements as well as the effectsof non-time-synchronized interfering signals. As before, a localoscillator 430 is modulated by the regenerated, synchronized PN code.The IF signal produced at the output of a receiving balanced mixer 440stage is both down-converted and despread; a bit-wise data demodulator450 then directly extracts the gated output stream. An optionalmultipath-amplitude detector block 460 can as above provide a relativemeasurement of the amount of multipath-caused disturbances in thereceived signal.

Example 3

Referring to FIGS. 5-6, a hybridfrequency-hopping/time-hopping/direct-sequence (FH/TH/DS)spread-spectrum scheme is depicted. The hybrid FH/TH/DS transmitter(FIG. 5) and receiver (FIG. 6) combine both FH/DS and TH/DS schemes toachieve more complex spreading distributions and afford even higher datasecurity than the simpler types; the specific circuit details followthose in the previous diagrams.

These hybrid (FH/TH/DS) types of systems are probably the most usefulfor practical burst-mode wireless-sensor devices for difficultindustrial RF environments. Alternatively, the bursts may be timed in aperiodic rather than pseudorandom manner (thus, obviously, eliminatingthe true TH modulation component) when system update rates need to behighly regular, or when standard periodic time-slotting is desired.

Although these depicted transmitter implementations employ final RFcarrier-frequency data-modulation methods, IF-modulation mayalternatively be efficiently utilized, particularly since many highlyintegrated DDS devices are available for popular IF frequency ranges(e.g., 70 MHz). Of course, the IF modulator in such systems will befollowed by a frequency-upconverting stage or subsystem to generate thefinal RF carrier. Dual-stage synthesizer architectures may-be requiredfor some IF-output DDS implementations to provide the full RF outputfrequency range when that exceeds available standard IF filterbandwidths. If should be noted that the various transmitter and receiverblock diagrams merely depict functional arrangements to illustrate thesignal-processing concepts; as such, they do not attempt to cover thecomplete range of configurations possible under the numerous aspectsand/or implementations of the invention.

Example 4

Referring to FIG. 7, a hybrid programmable DDS transmitter capable ofgenerating hybrid spread-spectrum signals is depicted. A frequencyaccumulator 700 is electrically coupled to an adder 705 and to itself700 (as feedback). A digital signal multiplexer (MUX) 710 is alsoelectrically coupled to the adder 705. The adder 705 is electricallycoupled to a phase accumulator 715. The phase accumulator 715 iselectrically coupled to: i) itself 715 (as feedback); ii) a phase adder(I) 720; and iii) a phase adder (Q) 725. The phase adder (I) 720 iselectrically coupled to a Sine ROM 730 of a phase-to-amplitude converter731. The phase adder (Q) 725 is electrically coupled to a Cosine ROM 735of the phase-to-amplitude converter 731.

Still referring to FIG. 7, the Sine ROM 730 of the phase-to-amplitudeconverter 731 is electrically coupled to an amplitude multiplier 740 andto a bypass circuit 780. The Cosine ROM 735 of the phase-to-amplitudeconverter 731 is electrically coupled to an amplitude multiplier 745 andto a bypass circuit 785. The bypass circuit 780 is electrically coupledto a MUX 750. The amplitude multiplier 740 is also electrically coupledto the MUX 750. The bypass circuit 785 is electrically coupled to a MUX755. The amplitude multiplier 745 is also electrically coupled to theMUX 755. The MUX 750 is electrically coupled to a DAC (I) 760. The DAC(I) 760 is electrically coupled to an LPF 770. The LPF 770 iselectrically coupled to an analog output (I) 790. The MUX 755 iselectrically coupled to a DAC (Q) 765. The DAC (Q) 765 is electricallycoupled to an LPF 775. The LPF 775 is electrically coupled to an analogoutput (Q) 795.

Still referring to FIG. 7, a set of lines utilized to control the hybridprogrammable DDS transmitter is also depicted. A delta-frequency wordline 701 is electrically coupled to the frequency accumulator 700. Adelta-frequency ramp-rate clock line 702 is electrically coupled to thefrequency accumulator 700. A set of frequency-control word lines 711 iselectrically coupled to the MUX 710. A main DDS clock line 716 iselectrically coupled to the phase accumulator 715. A phase-control word(I) line 721 is electrically coupled to the phase adder (I) 720. Aphase-control word (Q) line 726 is electrically coupled to the phaseadder (Q) 725. An amplitude control word (I) line 741 is electricallycoupled to the amplitude multiplier 740. An amplitude control word (Q)line 746 is electrically coupled to the amplitude multiplier 745. Anamplitude control word on/off (I) line 751 is electrically coupled tothe MUX 750. An amplitude control word on/off (Q) 752 is electricallycoupled to the MUX 755.

Example 5

Referring to FIG. 8, a hybrid programmable DDS transmitter with externalinterface is depicted. The configuration is similar to the one indescribed for FIG. 7, with the following modifications: the sine ROM 730is electrically coupled to an equalizer FIR filter 810 and to a bypasscircuitry 830. The cosine ROM 735 is electrically coupled to anequalizer FIR filter 820 and to bypass circuitry 840. The equalizer FIRfilter 810 is electrically coupled to a MUX 850. The bypass circuitry830 is also electrically coupled to the MUX 850. The equalizer FIRfilter 820 is electrically coupled to a MUX 860. The bypass circuitry840 is also electrically coupled to the MUX 860. The MUX 850 iselectrically coupled to the amplitude multiplier 740. The MUX 860 iselectrically coupled to the amplitude multiplier 745.

Still referring to FIG. 8, a set of lines utilized to control the hybridprogrammable DDS transmitter is similar to the one described for FIG. 7,with the following additions: an equalizer control word (I) 811 iselectrically coupled to the equalizer FIR filter 810. An equalizercontrol word (Q) 821 is electrically coupled to the equalizer FIR filter820. An equalizer control on/off (I) line 851 is electrically coupled tothe MUX 850. An equalizer control on/off (Q) line 852 is electricallycoupled to the MUX 860.

A high-speed external processor parallel logic interface 800 providesthe lines utilized to program the transmitter depicted in FIG. 8. Thehigh-speed external processor parallel logic interface 800 in essencetransfers device-parameter programming data from the DSP or othercontroller to the respective appropriate hardware subsystems to performthe specific modulation function(s) desired. To overcome typicalparallel-interface speed and/or pin-number limitations, some internalintermediate caching memory and perhaps decoding and/or timing logic(between the external interface and the synthesis blocks) is highlyuseful in helping to achieve high rates of DS chipping (spreading),frequency-hopping/chirping, and even data modulation, particularly whenimplementing more complex modulation formats (such as the denser QAMconstellations).

Additional features of the implementations of FIGS. 7-8 include theability to generate chirp or composite DS/chirp modulations withdownstream amplitude-modulation capabilities via the front-endfrequency-accumulator stage; here, a rate-of-sweep word andstart-frequency can be programmed into the frequency-control circuitry.The following phase-accumulator block with its phase-to-amplitudeconverter (sine/cosine ROMs) and amplitude multiplier (modulator) willthen output near-sinusoidal waves to the I- and Q-channel DACs in theselected IF-range frequency band. Further, the amplitude multipliers canalternatively (and preferably) be full four-quadrant multipliers, whichbesides reducing spectral splattering will also allow both positive andnegative amplitude variations (swings), and the option of downstreambinary phase-shift keying (which can be implemented via a simpleamplitude inversion or sign change).

Example 6

Referring to FIG. 9, a typical RF upconverter circuit used in digitaldata transmitters is depicted. The RF upconverter is utilized to convertthe quadrature (I and Q) analog signal outputs (such as from systems asdepicted in FIGS. 7 and 8) into RF signals such as those employed toimplement the present invention. A master clock 900 may be the sameclock indicated in previous figures or else a dedicated unit, which inconjunction with an RF frequency synthesizer 910 generates the final RFcarrier frequency. Two identical carrier-frequency signals feed a pairof balanced modulators 920,930. The balanced modulator 920 mixes the RFcarrier-frequency signal with the “I” analog intermediate-frequency (IF)output from the DDS circuit (depicted in FIG. 7 and FIG. 8). Thebalanced modulator 930 mixes the RF carrier-frequency signal with the“Q” analog intermediate-frequency (IF) output from the DDS circuit(depicted in FIG. 7 and FIG. 8).

Still referring to FIG. 9, a pair of signals from the balancedmodulators 920,930 is linearly added in the summing block 940 to producethe final quadrature-modulated RF spread data signal. A band-pass filter(BPF) 950 removes out-of-band energy (including RF harmonics and images)before feeding the signal into the linear RF power amplifier 960. Anamplitude control signal 970 derived from the system control hardwarealters the RF output power as desired, for power control, amplitudedithering/modulation, or both. The final output signal then feeds anantenna 980.

Example 7

Referring to FIG. 10, an alternate but well known “single-sideband” or“image-rejecting” RF upconverter arrangement is depicted. The RFupconverter is essentially identical to the circuitry of FIG. 9, exceptthat the RF frequency synthesizer 1000 provides two quadrature-phased(0° and −90°) carrier signals 1010,1020 to the two balanced modulators1030,1040, which in turn are fed by the “T” and “Q” analog IF signalsfrom the DDS circuitry (depicted in FIG. 7 and FIG. 8), respectively.Since the image-frequency component is largely cancelled at the summer's1050 output, a simple low-pass filter (LPF) 1060 maybe utilized in manyinstances to provide adequate RF spectral purity of the finaltransmitted signal.

Implementations of the corresponding receiver systems, despite theirfine-grained complexity, can in general architecturally follow theexamples of the previous figures.

Example 8

Referring to FIG. 11, a typical dual-polarization HSS transmitterimplementation incorporates a master clock 1100 to generate all requiredtiming signals from a common reference source, including the synthesizerreference signal 1101 (typically 10 MHz) and the spread-spectrumchipping clock frequency 1102, which drives the main system PNpolynomial code generator 1112. The code generator outputs a serialn-bit PN code chip-stream 1114 for the DS signal to XOR gate 1115, whichbinary-multiplies the chip-stream 1114 by the digital data inputsequence at 1116. The resulting BPSK spread-data stream at the XORoutput 1117 is then fed to balanced modulator 1130 to DS spread-spectrummodulate the RF carrier-frequency signal 1111. Meanwhile, the PNgenerator 1112, corresponding to the internal state of its internalbinary polynomial registers, also outputs a parallel m-bit word 1103 tothe RF frequency-synthesizer block 1110 which in part controls the RFoutput frequency at 1111. The remainder of the digital frequency-controldata is input from a p-bit wide bus 1104 from an external RFband-selection data source. The input words at 1103 and 1104 completelyspecify the instantaneous final RF carrier frequency generated bysynthesizer 1110, including the desired (usually pseudorandom)frequency-hopping pattern. The hopped signal exiting at 1111 is thenmultiplied by the DS component at balanced-modulator 1130 to generatethe composite FH/DS-format HSS signal at 1131. Unwanted harmonics andother spurious signals are removed by LPF 1132 and the signal is dividedinto two identical, typically equal-level components by splitter 1133.The two outputs signals from the splitter (1134, 1135) each feed again-controlled RF amplifier (1136, 1137) and in turn a singly polarizedantenna (1140, 1141) to transmit the vertically (V) and horizontally (H)polarized signals. A separate k-bit data word 1113 is extracted from thePN generator 1112 and feeds amplitude-control circuit 1120, which inturn digitally adjusts the output level of RF amplifier 1136 accordingto the value of the k-bit word via signal 1123. The k-bit data 1113 isalso presented to subtractor logic block 1122, which simply calculatesthe difference between word 1113 and a constant equal to 2^(k). Thisremainder value, which appears at 1121, represents the rest of theoutput power and is input to amplitude-control block 1121. In turn, thecontrol signal at 1124 alters the output of RF amplifier 1137; thus, thetotal combined power emitted from the V and H antennas remains constant,but the relative proportions allotted to the V- and H-polarized signalswill vary in a pseudorandom fashion according to the k-bit codeword1113. This dithering of the relative transmitted signal polarization isanother means of multipath mitigation and represents a further, highlyuseful aspect of the instant invention.

Example 9

Referring to FIG. 12 (and following from the basic implementation ofFIG. 2) a typical polarization-diversity HSS receiver according to anaspect of the invention is described. The respective V- and H-polarizedHSS signals are received in antennas 1200, 1201 at left, boosted by LNAs1202, 1203, and introduced to down-converting balanced mixers 1204,1205. The mixers are each fed with an FH/DS-modulated local oscillatorsignal 1206, generated in balanced-modulator block 1220. The twodiversity (V and H) input signals are down-converted to the desiredintermediate frequency (IF) via the balanced mixers, amplified andbandpass filtered in bandpass amplifier (BPA) blocks 1240, 1242,combined via gating, weighted or unweighted summing, maximal-ratiocombining, or other techniques in block 1250, and finally demodulated ina conventional manner in 1252 according to the type of data modulationemployed (ice., BPSK, QPSK, MSK, etc.). The combiner 1250 may alsoemploy a modified form of majority-logic directed feedback through thedemodulator 1252 to optimally combine the separate input V and Hsignals; alternatively, the demodulator could via two separate channelsindependently decode the V and H data signals before developing thefinal optimized result. Of course, the use of diversity antennas shouldnot considered in the invention to be constrained to two (V and H), butcould easily include additional received channels of both polarizationsto provide spatially diverse reception capability for improved signalreception efficiency, much as current CDMA cell-phone systems, which usemultiple-finger. “rake” receivers to deal with multipath signals.Conversely, the use of the V and H signal polarizations in the HSSreceiver could certainly include similar combining schemes to those ofthe “rake” architecture. A further option in the HSS receiver would beto utilize a combiner specifically optimized to handle theconstant-envelope signals produced by one specific variety of HSStransmitter. Since incidental multipath reflections invariably causespurious amplitude modulations (AM) in the received signals (though thetransmitted signal was nomionally of constant amplitude), the detectionof these amplitude variations can be explicitly employed to triggercorrector circuits which serve to minimize the incidental AM and therebyreduce the received-signal waveform distortion caused by the multipath.As in the transmitter above, m bits from the n-bit PN code generator(though typically offset by a fixed amount from those in the transmitterto provide the desired IF difference frequency) are used to select thedesired hopping channels within the selected RF receiving band. This isaccomplished by operating a master PN code generator 1230 essentiallyidentical to that in the HSS transmitter of FIG. 11 and extracting anm-bit parallel data bus (corresponding to the internal registers of thePN generator) to drive the RF frequency-synthesizer block 1212 with thehopping component of the full code. The serial chipping-code stream isoutput at 1231; this feeds one input of the DS balanced-modulator block1220. The synthesizer output at 1213 is mixed at 1214 with the output ofa typically fixed local oscillator 1210, which operates at an offset(the IF) from the nominal RF input center frequency to up-convert thesynthesizer to the desired RF band. Bandpass filter (BPF) 1215 removesthe undesired image component; the filtered output at 1216 is thenapplied to the balanced modulator 1220 to generate the desiredHSS-modulated (FH/DS) local oscillator signal at 1206.

This locally spread signal then (when properly synchronized)automatically despreads the DS portion of the incoming hybrid signal;the hopping of the local signal also removes the FH component, leaving asimple data-modulated single-frequency signal at the input to thebandpass IF amplifier chains 1240, 1242. Synchronization for the system1254 is derived from the data stream, the RF carrier frequency, or acombination thereof. Synchronization of the Master Clock 1259, PNGenerator 1230, and Local Oscillator 1210 are achieved through feedbacksignals 1255, 1256, and 1258 respectively. An optionalmultipath-amplitude detector block 1260, fed from the V and H IF outputs1241, 1243 (via lines 1244, 1245) can provide a relative measurement ofthe amount of multipath-caused disturbances in the received signal. Thisis typically implemented via detection of variations in thereceived-signal's envelope (amplitude), which are utilized by separatesignal-processing circuitry to estimate the multipath-induceddegradations in the incoming signal and perform at least a first-ordercancellation thereof to improve final data quality at the receiver'soutput. The final processed output of this multipath-estimation block isshown at 1261. An additional feature of the multipath detector is thatdynamic estimates of received-signal quality obtained therein can beutilized not only to adaptively improve reception of the incoming datastream but also (in an HSS transceiver scenario) to trigger dynamicoptimization of the outgoing HSS transmitter signal format (e.g., DS,FH, TH, and/or polarization parameters) to help counter both static anddynamic changes in thr RF channel environment.

Practical Applications of the Invention

Practical applications of the invention that have value within thetechnological arts include: wireless sensors and data networks inindustrial plants, offices, commercial buildings, and warehouses;environmental monitoring systems; container/asset/personnel tracking andtelemetry applications; wireless local-area networks (WLANs); medicaltelemetry, battlefield/tactical sensors; and secure data transmissionfor industrial, military, and national security applications, allequally valid for domestic and foreign markets. There are virtuallyinnumerable uses for the invention, all of which need not be detailedhere.

Advantages of the Invention

A hybrid spread-spectrum system, representing an embodiment of theinvention, can be cost effective and advantageous for at least thefollowing reasons. The invention improves quality and/or reduces costscompared to previous approaches. Other advantages can include: superiormultipath-rejection capabilities, improved data integrity/security,better low probability-of-detection/probability-of-interception(LPD/LPI) properties, lower link delay (latency) figures, superiornarrowband/wideband jamming resistance, fast synchronization, higheruser density, less mutual interference among users in a given area orfrequency band, increased statistical signal diversity (for betterrobustness), the superior near-far reception properties of FH (a majordrawback of pure-DS systems), and lower overall peak occupied bandwidths(less spectral “splatter”) as compared with most present spread-spectrumradio techniques. An additional key use of the HSS protocol is in thecombined (or separate) reader/interrogator units to extract data frompassive, semi-passive, semi-active, or fully active RF tags, commonlyknown as RFID tags. The use of HSS protocols in the tag reader units,which typically combine both interrogating (illuminating) RF transmitterand associated receiver-reader devices, will provide greater tag readingefficiencies than either standard DS or FH based systems, due to thegreater signal diversity of the HSS emissions. Whereas virtually allexisting tag readers have null or “dead” spots in their RFtag-interrogating fields, the constantly dithered HSS signal willstatistically have far fewer signal nulls and will thereby exhibit ahigher RF tag read efficiency, with fewer tag “no-reads”.

A greater appreciation of the benefits of the hybrid spread-spectrumsignaling technique of the invention can be had by examination of thetypical 915-MHz indoor RF delay profile of FIG. 13. In this environment,the signal-dispersion times range from roughly 10 to 250 ns, with amedian RMS dispersion value of about 46 ns. The longer values,corresponding to larger spaces or enclosed areas typical of industrialmanufacturing facilities, would imply a minimum spreading rate ofapproximately 4 Mchips/sec, while the shorter (worst-case) valuesencountered in offices or smaller rooms call for spreading rates of upto about 100 Mchips/sec (and, thus, at least 100 MHz of totaltransmitted signal bandwidth). Obviously, this latter requirementexceeds the available bandwidth in either the 915 or the 2450-MHz ISMbands and requires the full width of any of the three 5-GHz ISM/U-NIIbands allocated for unlicensed spread-spectrum transmissions in the U.S.Even in the latter case, to operate multiple full-band devices in thesame space would require careful coordination of the multiple users (viatime multiplexing or power-controlled code-division multiple-access[CDMA] techniques) to prevent significantly large numbers of collisionsand a consequential loss of data packets.

Compared with conventional direct-sequence or frequency-hoppingspread-spectrum systems, the hybrid technique of the invention offersimproved process gain, jamming margin, and multiple-access capabilities.In addition, the hybrid technique offers the advantages of the relativefreedom from near-far effects of FH as compared with conventional DS.Since in the hybrid system the DS component can be of lesser bandwidthfor comparable overall performance, the front-end and IF bandwidths ofthe hybrid receiver can be significantly-smaller (and thus possessgreater selectivity) than in the standard DS implementation, therebyoffering greater filter-based rejection of adjacent-channel,out-of-band, and spurious signals. Thus, the much higher amplitudes of anearby but off-channel transmitter will not cause the signal blockagesof the weaker (more-distant) desired on-channel signal typical ofconventional DS systems.

From Chapter 2 of the standard text Spread Spectrum Systems withCommercial Applications, 3rd Edition, by Robert C. Dixon, John Wiley &Sons, Inc., 1994, pp. 18-58, the classic equation for the generalizedprocess gain of a standard spread-spectrum (direct-sequence orfrequency-hopping with contiguous, non-overlapping channels) signal is:G _(p) =BW _(RF) ÷R _(info)where G_(p) is the effective processing gain, BW_(RF) is the total(two-sided) spread-spectrum RF signal bandwidth, and R_(info) is themodulating (pre-spreading) data rate or information bandwidth, also inthe total modulated (two-sided) representation. For standarddirect-sequence systems, the gain is in general equal to thespreading-code length; in the case of simple frequency-hopping systems,the (long-term average) processing gain for contiguous or non-contiguouschannel ensembles is simply equal to the total number of hoppingchannels. If we concurrently utilize both DS and FH methods, assumingthat the DS signal bandwidth is small compared to the width of the totalavailable RF band, so that there are a reasonably large number of hybridhopping channels, the overall hybrid-signal process gain is simply theproduct of the two individual process gains:G _(p(FH/DS)) =G _(p(FH)) ×G _(p(DS))In decibels, the equation becomes:G _(p(FH/DS)dB) =G _(p(FH)dB) +G _(p(DS)dB)=10 log(no. of hoppingchannels)+10 log(BW _(DS) /R _(info))where G_(p(FH/DS)) is the hybrid spread-spectrum process gain, G_(p(FH))is the frequency-hopping gain, and G_(p(DS)) is the straightdirect-sequence gain. In the theoretical limit, for a fixed availableband width (e.g., 26 MHz for the 902-928 MHz ISM band) andnon-overlapping FH channels, the composite process gain for the hybridDS/FH system cannot exceed the ratio of the total band width to theinformation rate. For instance, if one chose to send a standard datarate of 19.2 kb/s using a single DS signal occupying the entire band,then the maximum attainable in-band process gain using QPSK modulationwould be 26×10⁶÷19.2×10³≅1354≅31.3 dB. For full-band noise,interference, or jamming, then, hybrid DS/FH techniques usingnon-overlapping channel sets will not theoretically provide any moreprocess gain than for the single DS signal but will in practice still besuperior to the full-band DS format in rejecting multipath-inducederrors, in resolving near-far interference effects, and in permittingmultiple signals to be sent simultaneously within the confines of theselected band. [If, however, the FH channels are overlapped 50% (i.e.,by half the DS chipping rate), then the DS/FH system can actuallyachieve about double (+3 dB) the process gain of the straight-DSversion.] Further, as compared with conventional DS implementations, thehybrid SS systems will provide equivalent or better link performancewith lower composite chipping rates, slower hardware processing speeds,and generally reduced transmitting-device and receiver powerconsumption.

Concatenating coordinated time-hopping with the DS/FH hybrid method addsseveral additional modes of improved operational flexibility. In theusual sense, time hopping by itself does not provide process gain,assuming the receiver input is gated off during non-transmissionintervals; instead, an effective jamming gain or margin for continuousinterfering signals is afforded in a manner directly proportional to thesignal's duty cycle, i.e., the ratio of the transmitter (or receiver)“on” times to the total interval under consideration. Correspondingly,the effective “process gain” for intermittently interfering signals is(statistically) simply the product of the two signals' duty cycles. Theprincipal advantage in adding coordinated or code-synchronizedtime-hopping is in the improved system performance with multiple devicesin a shared. RF environment (the “multiple-access” scenario). Forexample, if there are several hundred sensor devices in a common area(e.g., a factory complex, high-rise office building, shipping terminalyard, etc.) which all need to send intermittent telemetry data to acentral receiver, the use of DS alone with random burst transmissionscan only succeed if the product of the number of devices and their RFburst lengths is relatively small compared to unity, i.e., the systemduty factor is <<100%. Otherwise, a large number of collisions willoccur and much data will be lost; frequent retransmissions will improvethe average system transmission reliability, but at the expense ofsignificantly lower aggregate data rates and wasted device energy. Theuse of code-division multiple access (CDMA) techniques can resolve mostof the collision problems but invariably adds significant complexity(and cost) to the system by adding major infrastructure components(i.e., base stations) and also forcing the addition of RF receivers,coders, and complex control hardware and algorithms to close therequired RF link power-control loop at each device. The massivecomplexity of the CDMA approach is generally cost-effective only in themass consumer cell-phone market due to the sheer numbers (tens ofmillions) of deployed units; for general low-power (battery-operated) RFtelemetry applications, especially including simple, inexpensivetransmit-only sensor and tag devices, the general DS/CDMA approach isneither power- nor cost-effective.

Another, more intuitive explanation of the advantages of the combinedFH/TH/DS signaling method of the invention follows. Suppose that twoindependent sensor/telemetry devices happen to transmit their data in acommon environment (e.g., a large factory) at the same time, using theFH/TH/DS technique. Assuming even that both are in the same group andhave the same assigned DS spreading code, each is programmed to select adifferent portion of that code to drive its onboard FH and TH circuitry;thus, each will (statistically) transmit at different frequencies and atdifferent times. Even if the two do transmit simultaneously,statistically they will be on different frequencies; if they use thesame hopping frequencies, they will statistically use them at disparatetimes. Assuming negligible noise levels, the effective probability of adata error due to a collision between two hybrid FH/TH/DS signals can becalculated as the product of: (1) the probability of a collision in thetime domain [i.e., the product of the two devices' randomized individualduty cycles]; (2) the probability of a frequency collision[approximately the product of the inverse of the lengths of theindividual FH control sequences, assuming non-overlapping hoppingchannels]; and (3) the cross-correlation power ratio of the two codes,assuming nearly equal signal powers at the receiver, as in the case ofpower-controlled CDMA systems. If there are unequal powers, the thirdterm [the DS separation ratio] will be somewhat degraded, by about 1 dBper 2.5 dB of received power deviation from the ideal (i.e., equal);thus, the effective error rate probability due to collision of the twosignals will be:P _(e) ≅P _(ec) =P _(ct) ·P _(cf) ·R _(cc)where the overall bit-error probability P_(e) in the absence ofsignificant background random noise and multipath effects is roughlyequal to P_(ec), the error due to collisions alone (i.e., a variant ofthe classical dominant multiple-access interference in CDMA cell-phonesystems); this is in turn simply the product of the respective collisionrates in time and frequency, given by P_(c), and P_(cf), with theeffective code-power separation ratio R_(cc) (power cross-product vs.self ratio) of the selected DS code versus its companion codes (e.g.,about 24 dB for an assumed order-10, 1024-length augmented Gold code).In the usual HSS application, asynchronous code sets such as MLS, Gold,and Kasami codes are preferred; the Walsh codes used in CDMA cell-phonesystems require fully synchronous (coherent) reception to achieveusefully low levels of code cross-correlation and thus demandsignificantly greater system complexity. For example, if the overallpolynomial length of each signal is 1024=2¹⁰, and the FH segment lengthis 64=2⁶ and the TH duty factor of both is 1/16, then the approximatetime-averaged probability of a single-hop collision between the two HSStransmissions is given by:( 1/16)·( 1/64)·(⅛)·( 1/64)·R _(cc)≈( 1/1024)·(1/512)·(10^(−2.4))≈7.58×10⁻⁹assuming good device power control. Obviously, the code separationprovides adequate isolation even if both devices transmit at the sametime (or partially overlapping times) and on the same frequency. [Theoverlapping time-slot scenario gives two opportunities for collision,thus causing a doubling of the nominal 1/16 TH factor for the seconddevice]. For multiple-hop transmissions, the expressions quickly becomevery complex and the mode of detection must also be included (i.e.,standard, majority-logic, soft-logic, etc.); for a full-systemcalculation, all user parameters (bit rates, chipping rates, hoppingrates, bandwidths, spreading-code correlation characteristics, devicepower levels, modulation/demodulation methods, etc.) must be consideredas well. For the multi-user case with k distinct devices, the HSS systemwill exceed the usual performance-levels for standard power-controlledDS-CDMA systems, as described by the standard equation formultiple-access bit-error probability:P _(e(DS))=½erfc[2/(k−1)·(f _(b) /f _(c))]^(1/2),where f_(b) and f_(c) are the bit and chip rates, respectively. Thecorresponding equation for the HSS case will also include terms for theFH (P_(cf)) and TH (P_(ct)) access statistics, which are highlydependent on the system's specific parameters but in general willdecrease the P_(e) figure by at least an order of magnitude (oftenmore):P _(e(HSS))=½erfc[2/(k−1)·(f _(b) /f _(c))]^(1/2) ·P _(cf) ·P _(ct)The jamming margin for the hybrid system is similarly complex but isstill comparably greater than that of its standard DS and FHcounterparts; in general, the jamming ratio is simply thespread-spectrum process gain minus implementation losses and therequired signal-to-noise ratio, so the HSS case is invariably morerobust to usual forms of interference or jamming.

As previously explained, the fast-hopping form of the HSS waveform(certain embodiments of which are referred to as “FastHSS”) can includethe specific code-related combination of standard direct-sequence (DS)spread-spectrum modulation with “fast” frequency hopping (FFH), whereinmultiple frequency hops occur within a single data-bit time. Again, themost significant benefit of this waveform is that each bit isrepresented by chip transmissions at multiple frequencies. If one ormore chips (or hops) are corrupted by multipath or interference in theRF link, a majority will statistically still be correct. Morespecifically, for the fast-hopping form of the HSS waveform, theimproved bit-error-rate is accomplished in the receiver by comparingbit-length cross-correlation functions with sub-bit-lengthcross-correlations on a bit-by-bit basis and utilizing whichever valueis optimum (e.g., has a higher correlation value). For example, if anHSS signal has a spreading length of N chips/bit and H hops/bit, thenthere are (N÷H) chips/hop. So, if one of the hops experiencesinterference due to multipath or jamming, then the other N−(N÷H) chipsare still available for establishing the value of that bit. In fact, ifeach group of x_(n)=(N÷H) chips, where [n=1, 2 . . . H] can be declaredvalid versus invalid, and only the valid groups used forcross-correlation, then the receiver's ability to correctly decode thatparticular bit is greatly enhanced. Typically, DSSS receivers make achip-by-chip determination of the phase of a carrier (assuming PSKmodulation) or they use multi-level logic (accumulation of thecorrelation sums) and perform a pseudo-bit-length integration. Byutilizing FastHSS, the receiver can dynamically (bit-by-bit) optimizethis trade-off, whereas existing-art DSSS systems or FH/DS systems thathop slower than once per bit cannot utilize this advantage.

Therefore, during tracking, each group of x_(n) chips arecross-correlated with the corresponding portion of the stored PN code.In parallel, the receiver logic performs a standard bit-lengthauto-correlation of the fall chipping sequence. If the standardauto-correlation function surpasses the detection threshold sufficientlyto recognize a valid data-bit result, then the subset cross-correlationfunctions are ignored. However, if the bit-length autocorrelation valueis insufficient for unambiguous data-bit detection, then the H subsetcross-correlation values are evaluated. If the threshold for bit-lengthcorrelation is assumed to be a·N, then the subset cross-correlationthresholds would be set to a·(N÷H). If i of the subset cross-correlationvalues are deemed sufficiently unambiguous then we concatenate thosesubsets and use a threshold of i·a·(N÷H), where i<H.

Analytically, we let S₁= cos [(ω₁+hω_(Δ))t]·m₁(t)d₁′(t) represent thereceived signal, where d₁′(t) represents the source-encoded data, m₁(t)represents the spreading code and cos [(ω₁+hω_(Δ))t] is the hoppedcarrier signal. Let the stored received waveform be represented asS₂=S₁+I+N₀, where I represents interference sources and N₀ representsadditive white Gaussian noise (AWGN). Thus, the autocorrelation functionfor the entire bit is:

${R(\tau)} = {\left( \frac{1}{T_{0}} \right){{\int\limits_{T_{0}}}^{\;}{{S_{1}(t)}{S_{2}\left( {t + \tau} \right)}\ {\mathbb{d}t}}}}$where T₀ is the bit-period and S_(i)(t) are periodic, and theautocorrelation function utilizing subsets is:

${R_{subsets}(\tau)} = {\sum\limits_{i = 1}^{H}\;{\left( \frac{1}{T_{0}/H} \right){\int_{t_{0} + {{({i - 1})}*{T_{0}/H}}}^{t_{0} + {i*{T_{0}/H}}}{{S_{1}(t)}{S_{2}\left( {t + \tau} \right)}\ {\mathbb{d}t}}}}}$In the case where there is no noise or interference,R(τ)=R_(subsets)(τ), and they both sufficiently surpass an unambiguousthreshold. However, in cases where at least one of the H frequenciesexperiences interference, either or both of these equations may not meetthe requirements for unambiguous bit detection. In this case, individualsubset cross-correlation functions are evaluated to determine which onesmeet the criteria:

${R_{i}(\tau)} = {{\left( \frac{1}{T_{0}/H} \right){\int_{t_{0} + {{({i - 1})}*{T_{0}/H}}}^{t_{0} + {i*{T_{0}/H}}}{{S_{1}(t)}{S_{2}\left( {t + \tau} \right)}\ {\mathbb{d}t}}}} \geq {a \cdot {N/H}}}$If any one of the R_(i)(τ) meet this criteria and all ambiguous R_(i)(τ)are removed, then the bit can be unambiguously detected by calculating:

${R_{subsets}(\tau)} = {{\sum\limits_{i = 1}^{H}\;{\left( \frac{1}{T_{0}/H} \right){\int_{t_{0} + {{({i - 1})}*{T_{0}/H}}}^{t_{0} + {i*{T_{0}/H}}}{{S_{1}(t)}{S_{2}\left( {t + \tau} \right)}\ {\mathbb{d}t}}}}} - {\sum\limits_{j = 1}^{k}\;{\left( \frac{1}{T_{0}/H} \right){\int_{t_{0} + {{({j - 1})}*{T_{0}/H}}}^{t_{0} + {j*{T_{0}/H}}}{{S_{1}(t)}{S_{2}\left( {t + \tau} \right)}\ {\mathbb{d}t}}}}}}$where there are k ambiguous subsets and j=b_(i) designate the individualambiguous subsets.

A simpler, more probabilistic approach to a more optimal detection ofFastHSS chips involves the use of majority logic, in which for the Hhops per bit, only slightly more than half need be correct. For H odd(i.e., H=2^(n)−1), the minimum number of correct hops (or chip groups)is 2^(n−1); for H even (e.g., H=2^(n)), the required minimum number is2^(n−1)+1. If we designate the number of total hops (chip groups)representing a single bit as H, then the total FastHss bit-errorprobability for hard binary-decision detection-can be expressed as:

$P_{e} = {\sum\limits_{x = r}^{H}\;{\left. (_{x}^{H}C \right){p^{x}\left( {1 - p} \right)}^{H - x}}}$where P_(e) is the total bit-error probability, H is the total number ofhops or chip-groups per bit, r is the minimum number of correct valuesper bit (for the majority-logic decision), C is the symbol for theprobabilistic combination (of H things taken x at a time), p is thesample (hop) error probability, and x is the index of summation. Forinstance, if we employ three hops for a data bit, then two sample (hop)decisions must be correct to avoid an error. Thus, for a basic p=10⁻²,p_(e) is 2.98×10⁻⁴; similarly, for p=10⁻³, P_(e)=2.998×10⁻⁶. If weinstead use 3 out of 5 hops for the decision, for a p of 10⁻³ we getP_(e)≈9.8×10⁻⁴ and for p=10⁻³, P_(e) becomes about 9.8×10⁻⁷. Clearly,the use of multiple hops and majority decision logic can yieldsignificant performance improvements over existing-art bit-detectionapproaches. Even greater advantage (>2 dB) can be gained in thisinstance by the use of soft-decision (multilevel) techniques, well knownin maximum-likelihood bit-detection schemes such as Viterbi decoders.

The terms a or an, as used herein, are defined as one or more than one.The term plurality, as used herein, is defined as two or more than two.The term another, as used herein, is defined as at least a second ormore. The terms “comprising” (comprises, comprised), “including”(includes, included) and/or “having” (has, had), as used herein, aredefined as open language (i.e., requiring what is thereafter recited,but open for the inclusion of unspecified procedure(s), structure(s)and/or ingredient(s) even in major amounts. The terms “consisting”(consists, consisted) and/or “composing” (composes, composed), as usedherein, close the recited method, apparatus or composition to theinclusion of procedures, structure(s) and/or ingredient(s) other thanthose recited except for ancillaries, adjuncts and/or impuritiesordinarily associated therewith. The recital of the term “essentially”along with the terms “consisting” or “composing” renders the recitedmethod, apparatus and/or composition open only for the inclusion ofunspecified procedure(s), structure(s) and/or ingredient(s) which do notmaterially affect the basic novel characteristics of the composition.The term coupled, as used herein, is defined as connected, although notnecessarily directly, and not necessarily mechanically. The term any, asused herein, is defined as all applicable members of a set or at least asubset of all applicable members of the set. The term approximately, asused herein, is defined as at least close to a given-value (e.g.,preferably within 10% of, more preferably within 1% of, and mostpreferably within 0.1% of). The term substantially, as used herein, isdefined as largely but not necessarily wholly that which is specified.The term generally, as used herein, is defined as at least approaching agiven state. The term deploying, as used herein, is defined asdesigning, building, shipping, installing and/or operating. The termmeans, as used herein, is defined as hardware, firmware and/or softwarefor achieving a result. The term program or phrase computer program, asused herein, is defined as a sequence of instructions designed forexecution on a computer system. A program, or computer program, mayinclude a subroutine, a function, a procedure, an object method, anobject implementation, an executable application, an applet, a servlet,a source code, an object code, a shared library/dynamic load libraryarid/or other sequence of instructions designed for execution on acomputer or computer system.

All the disclosed embodiments of the invention disclosed herein can bemade and used without undue experimentation in light of the disclosure.Although the best mode of carrying out the invention contemplated by theinventor(s) is disclosed, practice of the invention is not limitedthereto. Accordingly, it will be appreciated by those skilled in the artthat the invention may be practiced otherwise than as specificallydescribed herein.

Further, the individual components need not be combined in the disclosedconfigurations, but could be combined in virtually any configuration.Further, variation may be made in the steps or in the sequence of stepscomposing methods described herein.

Further, although the hybrid programmable DDS transmitter systemdescribed herein can be a separate module, it will be manifest that thehybrid programmable DDS transmitter system may be integrated into thesystem with which it is (they are) associated. Furthermore, all thedisclosed elements and features of-each disclosed embodiment can becombined with, or substituted for, the disclosed elements and featuresof every other disclosed embodiment except where such elements orfeatures are mutually exclusive.

It will be manifest that various substitutions, modifications, additionsand/or rearrangements of the features of the invention may be madewithout deviating from the spirit and/or scope of the underlyinginventive concept. It is deemed that the spirit and/or scope of theunderlying inventive concept as defined by the appended claims and theirequivalents cover all such substitutions, modifications, additionsand/or rearrangements.

The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” and/or “stepfor.” Subgeneric embodiments of the invention are delineated by theappended independent claims and their equivalents. Specific embodimentsof the invention are differentiated by the appended dependent claims andtheir equivalents.

1. A transmitter for generating a hybrid spread-spectrum signal totransmit data bits, wherein each of the data bits has a data bit time,the transmitter comprising: a pseudo-random code generator configured togenerate a first stream of pseudo-random code words and a second streamof pseudo-random code words, wherein the second stream of pseudo-randomcode words is generated as a function of the first stream ofpseudo-random code words to interrelate the second stream ofpseudo-random code words to the first stream of pseudo-random code wordsbased upon a predetermined relationship; a direct sequence generationcircuit configured to receive the data bits to be transmitted and thefirst stream of pseudo-random code words, the direct sequence generationcircuit configured to generate a direct sequence spread spectrum signalincluding a plurality of sub-sequences of chips for each of the databits based upon the first stream of pseudo-random code words; aprogrammable direct digital frequency synthesizer coupled to thepseudo-random code generator to receive the second stream ofpseudo-random code words, the programmable direct digital frequencysynthesizer configured to generate a carrier signal at a sequence ofcarrier frequencies for each of the data bits based upon a sequence ofthe pseudo-random code words of the second stream of pseudo-random codewords received by the programmable direct digital frequency synthesizerduring each data bit time; and a modulator in communication with thedirect sequence generation circuit and the programmable direct digitalfrequency synthesizer, the modulator configured to modulate the carriersignal with the direct sequence spread spectrum signal to generate adirect sequence fast frequency hopped spread spectrum signal.
 2. Thetransmitter of claim 1, wherein the sequence of carrier frequenciesgenerated by the programmable direct digital frequency synthesizerincludes a first carrier frequency and a second carrier frequency;wherein the direct sequence fast frequency hopped spread spectrum signalfor each of the data bits includes at least a first sub-sequence ofchips and a second subsequence of chips, and wherein the carrier signalat the first carrier frequency is modulated by the first sub-sequence ofchips and the carrier signal at the second carrier frequency ismodulated with the second sub-sequence of chips.
 3. The transmitter ofclaim 1, wherein the first stream of the pseudo-random code wordsincludes “n” bits per data bit time; wherein the second stream ofpseudo-random code words includes “m” bit frequency-hopping controlwords to produce “H” frequency hops per data bit time; and whereinn>m×H.
 4. The transmitter of claim 3, wherein each of the sub-sets ofchips includes the same number of chips per frequency hop.
 5. Thetransmitter of claim 1, wherein the direct sequence fast frequencyhopped spread spectrum signal corresponds to a respective data bit andincludes a sub-sequence of chips for each frequency of the carriersignal used to transmit the respective data bit.
 6. The transmitter ofclaim 1, wherein the predetermined relationship that interrelates thefirst stream of pseudo-random code words and the second stream ofpseudo-random code words is a first predetermined relationship; whereinthe pseudo-random code generator is further configured to generate athird stream of pseudo-random code words; and wherein the third streamof pseudo-random code words is generated as a function of a thirdpredetermined relationship and at least one of the first stream ofpseudo-random code words, the second stream of pseudo-random code words,or a combination thereof, and wherein the stream of third pseudo-randomcode words is interrelated by a second predetermined relationship to theat least one of the first stream of pseudo-random code words, the secondstream of pseudo-random code words, and the combination thereof.
 7. Thetransmitter of claim 6, further comprising: an amplification circuit incommunication with the modulator, the amplification circuit configuredto amplify the direct sequence fast frequency hopped spread spectrumsignal to generate an amplitude controlled direct sequence fastfrequency hopped spread spectrum signal based upon an amplificationcontrol signal.
 8. The transmitter of claim 7, further comprising anamplitude control circuit in communication with the pseudo-random codegenerator and the amplification circuit, the amplitude control circuitconfigured to dither the amplification control signal based upon thethird stream of pseudo-random code words.
 9. The transmitter of claim 6,wherein each of the first predetermined relationship and the secondpredetermined relationship include an interrelationship based upon atleast one of direct subsets of bits of the pseudo-random code generator,rolling code segments of the pseudo-random code generator, scrambling ofcode vectors of the pseudo-random code generator, and table-basedreassignments of bit-pattern relationships of the pseudo-random codegenerator, or a combination thereof.
 10. The transmitter of claim 6,wherein the pseudo-random code generator is further configured togenerate a pseudo-random coincidence gate control signal as a functionof at least one of the first stream of pseudo-random code words, thesecond stream of pseudo-random code words, the third stream ofpseudo-random code words by the third predetermined relationship, and acombination thereof, the transmitter further comprising: a coincidencegate coupled between the modulator and the amplification circuit, thecoincidence gate configured to receive the pseudo-random coincidencegate control signal from the pseudo-random code generator; and thecoincidence gate further configured to time gate the direct sequencefast frequency hopped spread spectrum signal based upon thepseudo-random coincident gate control signal.
 11. The transmitter ofclaim 6, wherein each of the first predetermined relationship, thesecond predetermined relationship, and the third predeterminedrelationship include an interrelationship based upon at least one ofdirect subsets, rolling code segments, scrambling of code vectors andtable-based reassignments of bit-pattern relationships, or a combinationthereof.
 12. The transmitter of claim 1, wherein the pseudo-random codegenerator is further configured to generate a pseudo-random coincidencegate control signal; the transmitter further comprising: a coincidencegate in communication with the modulator and the pseudo-random codegenerator, the coincidence gate configured to receive the directsequence fast frequency hopped spread spectrum signal and thepseudo-random coincidence gate control signal from the pseudo-randomcode generator; and wherein the coincidence gate is configured to timegate the direct sequence fast frequency hopped spread spectrum signalbased upon the coincident gate control signal to generate a time hoppeddirect sequence fast frequency hopped spread spectrum signal.
 13. Thetransmitter of claim 12, wherein the predetermined relationship thatinterrelates the first stream of pseudo-random code words and the secondstream of pseudo-random code words is a first predeterminedrelationship; and wherein the pseudo-random coincidence gate controlsignal is generated as a function of at least one of the first stream ofpseudo-random code words, the second stream of pseudo-random code words,and a combination thereof based upon a fourth predeterminedrelationship.
 14. The transmitter of claim 13, wherein the fourthpredetermined relationship includes an interrelationship based upon atleast one of direct subsets of bits of the pseudo-random code generator,rolling code segments of the pseudo-random code generator, scrambling ofcode vectors of the pseudo-random code generator, and table-basedreassignments of bit-pattern relationships of the pseudo-random codegenerator, or a combination thereof.
 15. The transmitter of claim 1,wherein the modulator is a balanced modulator.
 16. The transmitter ofclaim 1, wherein the programmable direct digital frequency synthesizeris further configured to receive a band select input signal; and whereinthe programmable direct digital frequency synthesizer is furtherconfigured to generate the carrier signal within a frequency band as afunction of the second stream of pseudo-random code words and the bandselect input signal.
 17. A transmitter for generating anelectromagnetically polarized hybrid spread spectrum signal to transmitdata bits, the transmitter comprising: a pseudo-random code generatorconfigured to generate a first stream of pseudo-random code words and asecond stream of pseudo-random code words, wherein the second stream ofpseudo-random code words is generated as a function of the first streamof pseudo-random code words to interrelate the first stream ofpseudo-randsom code words to the second stream of pseudo random codewords based upon a predetermined relationship; a programmable directdigital frequency synthesizer coupled to the pseudo random codegenerator to receive the second stream of pseudo-random code words, theprogrammable direct digital frequency synthesizer configured to directlygenerate a carrier signal having a carrier frequency based upon thesecond stream of pseudo-random code words, and wherein in response tothe second stream of pseudo-random code words, the programmable directdigital frequency synthesizer is further configured to hop the carrierfrequency of the carrier signal during a data bit time for each of thedata bits, wherein multiple carrier frequency hops occur within eachdata bit time; a balanced modulator in communication with theprogrammable frequency direct digital synthesizer, the modulatorconfigured to receive a direct sequence spread spectrum signal generatedwith the second stream of pseudo-random code words, and the balancedmodulator further configured to generate a fast frequency hopped directsequence spread spectrum signal as a function of the carrier signalhaving multiple carrier frequency hops during each data bit time as afunction of the first stream of pseudo-random code words; a firstantenna having a first polarization, the first antenna in communicationwith the balanced modulator, the first antenna configured to emit thefast frequency hopped direct sequence spread spectrum signal as a firstfast frequency hopped direct sequence spread spectrum signal with thefirst polarization; and a second antenna having a second polarization,the second antenna in communication with the balanced modulator, thesecond antenna configured to emit the fast frequency hopped directsequence spread spectrum signal as a second fast frequency hopped directsequence spread spectrum signal with the second polarization.
 18. Thetransmitter of claim 17, wherein the predetermined relationship includesan interrelationship based upon at least one of direct subsets of bitsof the pseudo-random code generator, rolling code segments of thepseudo-random code generator, scrambling of code vectors of thepseudo-random code generator, and table-based reassignments ofbit-pattern relationships of the pseudo-random code generator, or acombination thereof.
 19. The transmitter of claim 17, furthercomprising: a splitter coupled between the balanced modulator and thefirst antenna, and the splitter also coupled between the balancedmodulator and the second antenna, wherein the splitter is configured tosplit the fast frequency hopped direct sequence spread spectrum signalinto a first signal and a second signal; and wherein the first signal isemitted by the first antenna as the first fast frequency hopped directsequence spread spectrum signal and the second signal is emitted by thesecond antenna as the second fast frequency hopped direct sequencespread spectrum signal.
 20. The transmitter of claim 17, furthercomprising: a first RF amplifier coupled between the balanced modulatorand the first antenna, the first RF amplifier configured to amplify thefirst fast frequency hopped direct sequence spread spectrum signal witha first amplification level; and a second RF amplifier coupled betweenthe balanced modulator and the second antenna, the second RF amplifierconfigured to amplify the second fast frequency hopped direct sequencespread spectrum signal with a second amplification level.
 21. Thetransmitter of claim 20, further comprising: the pseudo-random codegenerator further configured to generate a third stream of pseudo-randomcode words; and an amplitude controller coupled to the pseudo-randomcode generator, the amplifier controller in communication with the firstRF amplifier and the second RF amplifier, wherein the amplifiercontroller is configured to dither the first amplification level and thesecond amplification level as a function of the third stream ofpseudo-random code words.
 22. The transmitter of claim 21, wherein thepredetermined relationship that interrelates the first stream ofpseudo-random code words and the second stream of pseudo-random codewords is a first predetermined relationship; and wherein the thirdstream of pseudo-random code words is generated as a function of atleast one of the first stream of pseudo-random code words, the secondstream of pseudo-random code words, and a combination thereof based upona second predetermined relationship.
 23. The transmitter of claim 22,wherein each of the first predetermined relationship and the secondpredetermined relationship includes an interrelationship based upon atleast one of direct subsets of bits of the pseudo-random code generator,rolling code segments of the pseudo-random code generator, scrambling ofcode vectors of the pseudo-random code generator, and table-basedreassignments of bit-pattern relationships of the pseudo-random codegenerator, or a combination thereof.
 24. The transmitter of claim 17,wherein the first amplification level and the second amplification levelare dithered at a rate greater than a reflection coefficient of amultipath condition.
 25. The transmitter of claim 17, furthercomprising: a first RF amplifier coupled between the balanced modulatorand the first antenna, the first RF amplifier configured to amplify thefirst fast frequency hopped direct sequence spread spectrum signal witha first amplification level; a second RF amplifier coupled between thebalanced modulator and the second antenna, the second RF amplifierconfigured to amplify the second fast frequency hopped direct sequencespread spectrum signal with a second amplification level; and anamplitude controller coupled to the pseudo-random code generator, theamplitude controller in communication with the first RF amplifier andthe second RF amplifier, wherein the amplitude controller is configuredto adjust the first amplification level relative to the secondamplification level to maintain a relative power ratio between the firstfast frequency hopped direct sequence spread spectrum signal and thesecond fast frequency hopped direct sequence spread spectrum signal. 26.The transmitter of claim 17, wherein the direct sequence fast frequencyhopped spread spectrum signal for each of the data bits includes atleast a first sub-sequence of chips and a second subsequence of chips;wherein the sequence of carrier frequencies includes a first carrierfrequency and a second carrier frequency; and wherein the carrier signalat the first carrier frequency is modulated by the first sub-sequence ofchips and, subsequently, the carrier signal at the second carrierfrequency is modulated by the second sub-sequence of chips.
 27. Thetransmitter of claim 17, wherein the first stream of pseudo-random codewords generated with the pseudo-random code generator includes a “n” bitpseudo-random codeword per data bit time; and wherein the second streamof pseudo-random code words generated with the pseudo-random codegenerator includes a plurality of “m” bit frequency-hopping controlwords to produce “H” frequency hops per data bit time; and whereinn>m×H.
 28. The transmitter of claim 27, wherein each of the sub-sets ofchips includes the same number of chips per frequency hop.
 29. Thetransmitter of claim 17, wherein the first polarization and the secondpolarization are linearly polarized.
 30. A transmitter capable ofgenerating a fast frequency hybrid spread-spectrum signal to transmit aplurality of data bits, each of the data bits having a data bit time,the transmitter comprising: a pseudo-random code generator configured togenerate a first stream of pseudo-random code words, a second stream ofpseudo-random code words, and a third stream of pseudo-random codewords, wherein pseudo-random code words included in the second stream ofpseudo-random code words and the pseudo-random code words included inthe third stream of pseudo-random code words are a function of thepseudo-random code words included in the first steam of pseudo-randomcode words based upon a predetermined relationship; a direct sequencegeneration module in communication with the pseudo-random codegenerator, the direct sequence generation module configured to receivethe data bits to be transmitted and the first stream of pseudo-randomcode words, the direct sequence generation module further configured togenerate a plurality of chips as a plurality of sub-sequences of chipsfor each of the received data bits based upon the first stream ofpseudo-random code words; a programmable direct digital frequencysynthesizer in communication with the pseudo-random code generator toreceive the second stream of pseudo-random code words, the programmabledirect digital frequency synthesizer configured to generate a carriersignal based upon the second stream of pseudo-random code words; whereinin response to the second stream of pseudo-random code words, theprogrammable direct digital frequency synthesizer is further configuredto hop the carrier signal during each data bit time of each of therespective data bits, wherein multiple carrier frequency hops occurwithin each data bit time to generate a plurality of pseudo-randomcarrier frequencies as a sequence of carrier frequencies; a balancedmodulator in communication with the direct sequence generation circuitand the direct programmable frequency synthesizer, the balancedmodulator configured to modulate the carrier signal with chips, whereinfor each of the pseudo-random carrier frequencies, the carrier signal ismodulated by a respective sub-sequence of the chips of the plurality ofsub-sequences of chips, to generate a fast frequency hopped directsequence spread spectrum signal; and a coincidence gate coupled to thepseudo-random code generator and the balanced modulator, the coincidencegate configured to gate the fast frequency hopped direct sequence spreadspectrum signal as a function of the third stream of pseudo-random codewords to generate a time hopped fast frequency hopped direct spreadspectrum signal.
 31. The transmitter of claim 30, wherein thepseudo-random code generator is further configured to generate a fourthstream of pseudo random code words as a function of at least one of thepseudo random codes words of the first stream, the second stream, thethird stream, and a combination thereof based upon a known relationship,the transmitter further comprising: an amplifier in communication withthe coincident gate and configured to receive the time hopped fastfrequency hopped direct sequence spread spectrum signal, wherein theamplifier is further configured to amplify the time hopped fastfrequency hopped direct sequence spread spectrum signal based upon anamplification control signal; and an amplitude controller including anamplitude control input coupled to the pseudo-random code generator toreceive the fourth stream of pseudo random code words, and the amplitudecontroller further including the amplification control signal incommunication with the amplifier, wherein the amplitude controller isfurther configured to dither the amplification of the time hopped fastfrequency hopped direct sequence spread spectrum signal based upon inresponse to the fourth stream of pseudo random code words.
 32. Thetransmitter of claim 30, wherein the first stream of pseudo-random codewords, the second stream of pseudo-random code words, and the thirdstream of pseudo-random code words are interrelated by a polynomialfunction which is also known at a receiver of the time hopped fastfrequency hopped direct spread spectrum signal.
 33. A method forgenerating a hybrid spread spectrum signal to transmit a plurality ofdata bits, wherein each of the data bits has a data bit time, the methodcomprising: generating a first stream of pseudo-random code words with apseudo-random number generator; generating, with the pseudo-randomnumber generator, a second stream of pseudo-random code words as afunction of the first set of pseudo-random code words based upon apredetermined relationship wherein there are “H” pseudo-random codewords per data bit time; generating a spread spectrum signal thatincludes a plurality of sub-sets of chips, each of the sub-sets of chipsincluding at least three chips, for each of the data bits to betransmitted based upon the first stream of pseudo-random code words;generating, with a programmable direct digital frequency synthesizer, asequence of “H” carrier signals per data bit time, each of the carriersignals having a pseudo-random carrier frequency, based upon the secondstream of pseudo-random code words; and modulating each of the carriersignals with a respective sub-set of chips from among the plurality ofsub-sets of chips to generate a fast frequency hopped spread spectrumsignal.
 34. The method of claim 33, wherein generating the first streamof pseudo-random code words with the pseudo-random number generatorfurther comprises: generating a “n” bit pseudo-random codeword per databit time; and wherein generating the second stream of pseudo-random codewords as a function of the first set of pseudo-random code words basedupon the predetermined relationship further includes: generating “m” kitfrequency-hopping control words to produce “H” frequency hops per databit time; and wherein n>m×H.
 35. The method of claim 33, wherein each ofthe sub-sets of chips includes the same number of chips per frequencyhop.
 36. The method of claim 33, further comprising: generating a thirdstream of pseudo-random code words; and dithering an amplitude of thefast frequency hopped spread spectrum signal as a function of the thirdstream of pseudo-random code words.
 37. The method of claim 36, whereinthe predetermined relationship used to generate the second stream ofpseudo-random code words as a function of the first pseudo-random numbergenerator is a first predetermined relationship; and wherein the thirdstream of pseudo-random code words is a function of at least one of thefirst stream of pseudo-random code words, the second stream ofpseudo-random code words, and a combination thereof based upon a secondpredetermined relationship.
 38. The method of claim 36, wherein each ofthe first predetermined relationship and the second predeterminedrelationship are interrelated by at least one of direct subsets of bitsof the pseudo-random code generator, rolling code segments of thepseudo-random code generator, scrambling of code vectors of thepseudo-random code generator, and table-based reassignments ofbit-pattern relationship of the pseudo-random code generator, or acombination thereof.
 39. The method of claim 36, further comprising:generating a fourth stream of pseudo-random code words; and time gatingthe dithered fast frequency hopped spread spectrum signal as a functionof the fourth stream of pseudo-random code words to generate a hybridspread spectrum signal.
 40. The method of claim 36, wherein generatingthe fourth stream of pseudo-random code words comprises: generating thefourth stream of pseudo-random code words as a function of at least oneof the first stream of pseudo-random code words, thesecond-pseudo-random code words, and a combination thereof based uponthe predetermined relationship.
 41. The method of claim 40, whereingenerating the third stream of pseudo-random code words comprises:generating the third stream of pseudo-random code-words as a function ofat least one of the first stream of pseudo random code words, the secondstream of pseudo-random code words, the fourth stream of pseudo-randomcode-words, and a combination thereof based upon the predeterminedrelationship.
 42. The method of claim 36, wherein the spread spectrumsignal is a direct sequence spread spectrum signal.
 43. The method ofclaim 33, further comprising: generating an additional stream ofpseudo-random code words; and time gating the fast frequency hoppedspread spectrum signal as a function of the additional stream ofpseudo-random code words to generate a hybrid spread spectrum signal.44. The method of claim 33, wherein the additional stream ofpseudo-random code words is generated as a function of at least one ofthe first stream of pseudo-random code words, the second stream ofpseudo-random code words, and a combination thereof based upon apredetermined functional relationship.
 45. The method of claim 33,wherein the first stream and the second stream of pseudo-random codewords are functionally interrelated by one or more relationships basedupon at least one of direct subsets of bits of the pseudo-random codegenerator, rolling code segments of the pseudo-random code generator,scrambling of code vectors of the pseudo-random code generator, andtable-based reassignments of bit-pattern relationships of thepseudo-random code generator, or a combination thereof.
 46. The methodof claim 45, wherein the spread spectrum signal is a direct sequencespread spectrum signal.
 47. The method of claim 33, further comprising:generating a pseudo-random dither control signal; splitting the fastfrequency hopped spread spectrum signal into a first component and asecond component, wherein the first component and the second componenthave substantially identical signal power; and dithering an amplitude ofat least one of the first component and the second component to controla polarization between the first component and the second componentbased upon the pseudo-random dither control signal.
 48. The method ofclaim 47, wherein dithering the amplitude of at least one of the firstcomponent and the second component to control the polarization betweenthe first component and the second component further comprises:controlling a power level of the first component and a power level ofthe second component to optimize signal diversity between the firstcomponent and the second component.
 49. The method of claim 33, furthercomprising: transmitting the fast frequency hopped spread spectrumsignal from a radio frequency tag.
 50. The method of claim 33, whereinthe spread spectrum signal is a direct sequence spread spectrum signal.51. A method for transmitting data bits in a high multipath environmentwith a hybrid spread spectrum signal, the method comprising: generatinga stream of pseudo-random codes comprising a plurality of bits;generating within a data bit time, with a programmable direct digitalfrequency synthesizer, a plurality of carrier signals, each of thecarrier signals having a respective pseudo-random carrier frequency as afunction of a first subset of bits of the stream of pseudo-random codes;and modulating each of the carrier signals generated during the data bittime, as a function of a second subset of bits of the stream ofpseudo-random codes, with a plurality of sub-segments of chips;generating a direct sequence fast frequency hopped spread spectrumsignal, wherein each of the sub-segments of chips modulates one of theplurality of carrier signal; and wherein the second sub-set of bits is afunction of the first sub-set of bits of the bits of the stream ofpseudo-random codes.
 52. The method of claim 51, further comprising:splitting the direct sequence fast frequency hopped spread spectrumsignal into a first direct sequence fast frequency hopped spreadspectrum signal and a second direct sequence fast frequency hoppedspread spectrum signal; linearly polarizing the first direct sequencefast frequency hopped spread spectrum signal and the second directsequence fast frequency hopped spread spectrum signal; transmitting thefirst direct sequence fast frequency hopped spread spectrum signal witha first antenna having a first polarization; and transmitting the seconddirect sequence fast frequency hopped spread spectrum signal with asecond antenna having a second polarization.
 53. The method of claim 51,wherein the functional relationship between the first subset of bits andthe second subset of bits is based upon a predetermined relationship tobe used at a receiver configured to receive the direct sequence fastfrequency hopped spread spectrum.
 54. The method of claim 53, furthercomprising: splitting the direct sequence fast frequency hopped spreadspectrum signal into a first direct sequence fast frequency hoppedspread spectrum signal and a second direct sequence fast frequencyhopped spread spectrum signal; linearly polarizing the first directsequence fast frequency hopped spread spectrum signal and the seconddirect sequence fast frequency hopped spread spectrum signal;transmitting the first direct sequence fast frequency hopped spreadspectrum signal with a first antenna having a first polarization; andtransmitting the second direct sequence fast frequency hopped spreadspectrum signal with a second antenna having a second polarization. 55.The method of claim 54, wherein transmitting the first direct sequencefast frequency hopped spread spectrum signal with the first antenna andtransmitting the second direct sequence fast frequency hopped spreadspectrum signal with the second antenna further comprises: dithering anamplitude of at least one of the first direct sequence fast frequencyhopped spread spectrum signal and the second direct sequence fastfrequency hopped spread spectrum signal.
 56. A method of claim 54,wherein transmitting the first direct sequence fast frequency hoppedspread spectrum signal with the first antenna and transmitting thesecond direct sequence fast frequency hopped spread spectrum signal withthe second antenna further comprises: generating a first amplitudecontrol signal and a second amplitude control signal based upon thestream of pseudo-random codes; modulating an amplitude of the firstdirect sequence fast frequency hopped spread spectrum signal based uponthe first amplitude control signal; and modulating an amplitude of thesecond direct sequence fast frequency hopped spread spectrum signalbased upon the second amplitude control signal.
 57. The method of claim56, wherein the transmitted first direct sequence fast frequency hoppedspread spectrum signal and the transmitted second direct sequence fastfrequency hopped spread spectrum signal have a combined power level, themethod further comprising: controlling the first amplitude controlsignal relative to the second amplitude control signal to maintain adesired emitted power level envelope of the combined power level. 58.The method of claim 56, wherein modulating the amplitude of the firstdirect sequence fast frequency hopped spread spectrum signal based uponthe first amplitude control signal and modulating the amplitude of thesecond direct sequence fast frequency hopped spread spectrum signalbased upon the second amplitude control signal further comprises:dithering the amplitude of the first direct sequence fast frequencyhopped spread spectrum signal and the amplitude of the second directsequence fast frequency hopped spread spectrum signal at a rate at leastequal to an estimated rate of successively received reflected signals.59. The method of claim 51, further comprising: generating a coincidentgate control signal based upon a third subset of the bits of the streamof pseudo-random codes; gating transmission of the first direct sequencefast frequency hopped spread spectrum signal and the second directsequence fast frequency hopped spread spectrum signal based upon thecoincident gate control signal to time hop the transmitted first directsequence fast frequency hopped spread spectrum signal and thetransmitted second direct sequence fast frequency hopped spreadspectrum, and wherein the third subset of bits is a function of at leastone of the first subsets of bits, the second subset of bits, and acombination thereof.
 60. The method of claim 59, further comprising:interrelating the first subset of bits of the pseudo-random codes, thesecond subset of bits of the pseudo-random codes, and the third subsetof bits of the pseudo-random codes based upon a known relationship atthe receiver.
 61. The method of claim 59, wherein at least two of thefirst subset of bits, the second subset of bits and the third subset ofbits are programmably related by one or more relationships based upon atleast one of direct subsets of bits of the pseudo-random code generator,rolling code segments of the pseudo-random code generator, scrambling ofcode vectors of the pseudo-random code generator, and table-basedreassignments of bit-pattern relationships of the pseudo-random codes ofthe pseudo-random code generator, or a combination thereof.
 62. A methodfor transmitting data in a high-multipath environment, the methodcomprising: generating a first stream of pseudo-random codes having afirst sequence length based upon predetermined interrelationshipsbetween the first stream of pseudo random codes, a second stream ofpseudo-random codes and a third stream of pseudo random codes;generating the second stream of pseudo-random codes having a secondsequence of codes, as a function of the first stream of pseudo-randomcodes length that is longer than the first sequence length based uponthe predetermined interrelationships; generating a third stream ofpseudo-random codes as a function of at least one of the first stream ofpseudo-random codes, the second stream of pseudo-random codes or acombination thereof, based upon the predetermined interrelationships;generating multiple carrier frequencies within the data bit time with aprogrammable direct digital frequency synthesizer based upon the secondstream of pseudo-random codes to produce a fast frequency hopped carriersignal having “H” frequency hops per each data bit time; generating adirect sequence spread spectrum signal representative of the data basedupon the first stream of pseudo-random codes, wherein the directsequence spread spectrum signal includes “n” chips, and wherein “n” isevenly divisible by “H”; modulating the fast frequency hopped carriersignal with the direct sequence spread spectrum signal to form a fastfrequency hopped direct sequence spread spectrum signal; and gating thefast frequency hopped direct sequence spread spectrum signal based uponthe third stream of pseudo random codes to generate a hybrid spreadspectrum signal.
 63. The method of claim 62, wherein generating multiplecarrier frequencies within the data bit time with the programmabledirect digital frequency synthesizer based upon the second stream ofpseudo-random codes to produce a fast frequency hopped carrier signalfurther comprises: frequency sweeping the programmable direct digitalfrequency synthesizer to generate the fast frequency hopped carriersignal.
 64. The method of claim 62, further comprising: modulating anamplitude of the hybrid spread spectrum signal based upon a fourth steamof pseudo-random codes.
 65. The method of claim 62, wherein thepredetermined relationships that interrelate the respective codes of thefirst stream of pseudo random codes, the second stream of pseudo randomcodes, and the third stream of pseudo random codes are based upon atleast one of direct subsets of bits of the pseudo-random code generator,rolling code segments of the pseudo-random code generator, scrambling ofcode vectors of the pseudo-random code generator, and table-basedreassignments of bit-pattern relationships of the pseudo-random codegenerator, or a combination thereof.
 66. The method of claim 62, furthercomprising: splitting the hybrid spread spectrum signal into a pluralityof component signals, wherein each of the component signals issubstantially identical in amplitude; and modulating the amplitude of atleast one of the plurality of component signals to control polarizationof plurality of components based upon at least one pseudo-randomsequence of amplitude control words.